The present invention relates to a bus structure which enables various video signal processors to be divided into a plurality of function modules which in turn may be readily combined for video signal processing. The term "video signal processor" covers (i) an image memory for inputting and outputting a video signal at a video signal display speed and (ii) a unit capable of processing a video signal at a video signal display speed. The former is generally called a frame buffer and the latter, a video effector. These terms will be employed hereinafter.
In a video signal processor bus with divided functional modules, conventionally employed are
(1) a system with a processor bus being used as a nucleus; and
(2) a system with respective functional modules being interconnected as needs demand.
In the system (1), the processor bus includes address and data signals and writes and reads data through the data signal at an address addressed by the address signal. The system (1) is called in this specification a processor bus system a typical example of which is a frame buffer with peripheral devices around a video memory being arranged into a single module, which enables the memory capacity to be increased as needs demand by adding a further module or modules.
The system (2) has no concept of a bus. An actual circuit is straightforwardly functional-divided into functional modules which are interconnected with wiring as needs demand. Video effectors are of such construction. The system (2) is hereinafter called a no-bus system.
In the processor bus system, the video signal processor is functionally divided such that the processor plays a main roll, resulting in less flexibility as to addition of a new function or functions. For example, when an overlay function for displaying a picture plane through superimposition is required in an existing frame buffer, mere addition of a new functional module or modules is unsatisfactory to attain the task. It follows therefore that all of possibly required functions must be originally included in designing a processor bus type commercial frame buffer. This may mean that, when buying a frame buffer, a user pays a price which includes cost for some functions never used by the user. In addition, if the user wants a new additional function or functions, he/she must buy a new frame buffer.
Conversely, a no-bus system may readily receive a new functional module or modules. The system is however defective in versatility of respective functional modules for lack of the concept of the bus. For instance, incorporation of a functional module for a video effector into another video effector is next to impossible to do unless originally intendedly designed. It follows therefore that functional modules for no-bus systems are produced in more kinds and less quantity, which fact will cause video effectors to be generally very expensive.
The conventional systems have these demerits.